A new inexpensive, room temperature method for a one-part, conductive, stretchable, and flexible CNT-silicone 3D printable ink

Significance 

Personalized health monitoring is an exciting and rapidly expanding field that has the potential to revolutionize the way we manage our health. The primary objective of personalized health monitoring is to provide individuals with real-time information about their health status, empowering them to make informed decisions regarding their care. However, one of the key challenges in this field is the development of wearable sensors that are comfortable, affordable, and easy to use. Traditional wearable sensors are often bulky, uncomfortable, and expensive to manufacture. Thankfully, 3D printing technology holds great promise for addressing these challenges. By enabling the rapid and cost-effective fabrication of complex structures with high precision, 3D printing offers a potential solution for creating wearable sensors that are comfortable, affordable, and user-friendly. Carbon nanotubes (CNTs) have emerged as a promising material for the development of wearable sensors. CNTs possess exceptional properties such as high conductivity and flexibility, which make them ideal for integration into 3D printed structures. This capability allows for the fabrication of wearable sensors capable of monitoring various physiological parameters like heart rate, blood pressure, and temperature.

In a recent study published in the journal Advanced Functional Materials, researchers Andy Shar, Phillip Glass, and Professor Daeha Joung from Virginia Commonwealth University, in collaboration with Dr. Sung Park from the Korea Institute of Industrial Technology, set out to develop and thoroughly characterize a one-part, highly conductive, flexible, and stretchable carbon nanotube (CNT)-silicone composite that could be 3D printed. The research team successfully developed an ink that met all the desired criteria, demonstrating high conductivity, flexibility, stretchability, and biocompatibility suitable for health monitoring applications.

The researchers achieved this by dispersing carbon nanotubes in a silicone precursor and employing sonication to create a one-part CNT-silicone ink. Notably, this ink exhibited remarkable conductivity and a low percolation threshold of carbon nanotubes. It could be directly printed onto diverse substrates like glass, paper, fabric, and even skin without requiring any surface modification or adhesion promoter. Additionally, the ink allowed for the creation of self-supporting structures with intricate geometries, such as helices, coils, and pyramids, and high aspect ratios. After curing under ambient conditions within 24 hours, the ink formed a flexible and stretchable composite that exhibited heightened sensitivity to both tensile and compressive stimuli. The composite also demonstrated high thermal conductivity and a low thermal expansion coefficient.

Furthermore, the composite acted as a heating element capable of generating heat up to 80 °C with a 5V voltage, maintaining a stable temperature for over 10 minutes. It also proved valuable for water distillation, as it could evaporate water and produce pure water. Additionally, the composite functioned as a dual temperature sensor and Joule heating element, accurately measuring temperature changes of external heat sources and regulating its own temperature by employing different voltages. The composite’s applications extended to fabricating wearable electronics for health monitoring, including motion detection, cardiac monitoring, and respiratory monitoring. Impressively, it demonstrated good biocompatibility with human skin cells, causing no irritation or inflammation upon attachment. Moreover, the composite showcased exceptional durability during repeated bending, stretching, washing, and wearing tests, making it a promising candidate for personalized health tracking and bionic skin applications. This capability allows for the printing of patient-specific patterns and shapes directly onto the skin.

However, it is important to note that while increasing the carbon nanotube loading significantly enhances the electrical conductivity of the CNT-silicone ink, it simultaneously decreases its mechanical properties. Consequently, optimizing the carbon nanotube loading is crucial to achieve the desired balance between electrical conductivity and mechanical performance. To ensure its suitability for health monitoring applications, the researchers conducted biocompatibility tests in vitro, confirming that the CNT-silicone ink poses no harm to patients. They also employed the ink in 3D printing a wide range of sensors and devices, such as ECG and EEG electrodes, pressure sensors, temperature sensors, and a wearable device capable of simultaneously monitoring multiple physiological parameters. These outcomes highlight the potential of 3D printing conductive elastomers for personalized health monitoring applications.

The developed one-part CNT-silicone ink is a versatile material with extensive applications, offering the ability to 3D print a wide array of sensors and devices. Furthermore, its biocompatibility makes it suitable for use in implantable devices. The research team is actively working on refining the CNT-silicone ink for health monitoring applications, with a focus on improving its electrical and mechanical properties. They are also exploring new methods for 3D printing conductive elastomers and investigating the ink’s potential in other areas such as wearable electronics and robotics.

In conclusion, this groundbreaking research has successfully developed a one-part CNT-silicone ink that is highly conductive, flexible, stretchable, and 3D printable. The ink can be printed on various substrates and used to create self-supporting structures with high aspect ratios and intricate geometries. The resulting composite exhibits high sensitivity to mechanical and thermal stimuli, and it can function as a heating element, water distiller, and dual temperature sensor. Moreover, the composite is biocompatible, durable, and suitable for fabricating wearable electronics for health monitoring and bionic skin applications. The ongoing efforts of the research team continue to refine and optimize the CNT-silicone ink for personalized health monitoring applications, highlighting its potential to transform the field of healthcare.

A new inexpensive, room temperature method for a one-part, conductive, stretchable, and flexible CNT-silicone 3D printable ink - Advances in Engineering

About the author

Daeha Joung 

Assistant Professor of Physics
Virginia Commonwealth University

The Joung group focuses on developing a smart platform of advanced functional devices for diverse applications in 3D biomedical and nano-electronic fields that permit the manufacturing of complex multi-material, multi-scale, and/or multi-functional 3D devices. The group also has considerable research interests in bioprinting and origami-inspired self-folding to test new therapeutic options.

Reference

Shar A, Glass P, Park SH, Joung D. 3D Printable OnePart Carbon NanotubeElastomer Ink for Health Monitoring Applications. Advanced Functional Materials. 2023 ;33(5):2211079.

Go To Advanced Functional Materials

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